The present invention relates to an optical disk and a process for producing an optical disk. More particularly, the present invention relates to a process for producing an optical disk of the air sandwich structure in which two disk substrates having a recording layer made of an organic dye film are bound together via a spacer with the recording layer facing inside.
Optical disks of the air sandwich structure type contemplated by the present invention have conventionally been produced by the following steps:
(1) A polyacrylic disk substrate is cleaned and a grooved transfer layer is formed on the cleaned surface. A typical method for forming such a receiving layer consists of dripping a polyacrylic uv curable resin on a grooved metal stamper, super-posing an acrylic disk substrate on the stamper, uniformly spreading the uv curable resin over the substrate, irradiating the film of the resin with ultraviolet radiation to cause its polymerization, and peeling off the substrate from the metal stamper. As shown in FIG. 1(a), this process produces an assembly in which a transfer layer 2 is formed on the disk substrate 1.
(2) In the next step, an organic dye solution conditioned to a predetermined concentration is provided and spin-coated onto the transfer layer 2 to form a recording layer 3 of an organic dye film (FIG. 1(b)).
(3) Two disk substrates having such a recording layer 3 are superposed on each other via a spacer 4 with each recording layer 3 facing inside, and an adhesive agent 5 is applied to that area of each disk substrate which faces the spacer 4, followed by bonding the two disk substrates together to produce an optical disk of the air sandwich structure shown in FIG. 1(c).
As will be apparent from the above, the optical disk produced by the conventional process has an adhesive agent left on each of the recording layers in the area where the disk substrates are bonded to the spacer. Therefore, the overall bonding strength of the disk depends on the strength of adhesion between the polyacrylic base of the disk substrate and the transfer layer, the strength of adhesion between the transfer layer and the recording layer, the bonding strength between the recording layer and the adhesive agent, and also on the bonding strength between the adhesive agent and the spacer. The strength of adhesion between the transfer layer and the recording layer is weaker than the adhesion or bonding in other portions and peeling has frequently occurred at the interface between these layers.
The present invention solves the aforementioned problems of the prior art and the principal object of the invention is to provide a process for producing an optical disk that has an improved strength of adhesion between disk substrates at the area where peeling has often occurred.